Pressure monitoring method for roller hemming

ABSTRACT

A pressure monitoring robotic roller hemming apparatus includes a roller hemming tool having a compressible fluid shock absorber. A control panel is in fluid communication with the shock absorber. A pressure monitor is in fluid communication with the control panel and the shock absorber. The pressure monitor is operative to monitor pressure in the shock absorber.

TECHNICAL FIELD

This invention relates to robotic roller hemming, such as edge hemming of vehicle closure panels, and more particularly to a method of monitoring pressure in a robotic roller hemming apparatus.

BACKGROUND OF THE INVENTION

It is known in the vehicle closure panel hemming art that robotic roller hemmers can be used to roller hem the edges of nested metal panels such as automotive vehicle door panels, hood panels, and decklid panels.

Conventionally, roller hemming apparatus may be mounted to a multi-axis controllable robot and may include a hem roller carried by a support. The conventional hemming apparatus is adapted for hemming a bent portion of a workpiece, such as a door panel, positioned on a hemming die, by rotating the hem roller under pressure along the bent portion. The conventional roller type hemming apparatus can thus be used for continuous hemming along the contour of the edge of the workpiece.

In order to achieve good hemming with such a conventional roller hemming apparatus, the robot must move the hem roller along the edge of the workpiece at a generally constant distance from the hemming die. The robot is not composed of a perfectly rigid body, and when the hem roller is positioned against the edge of the workpiece, the robot arm or the hem roller may be deflected by its own resiliency or by a repulsive force exerted by the edge of the workpiece itself. For example, the edge of the workpiece may have inconsistent material dimensions such as bumps that exert a repulsive force on the robot. This results in interruption of the pressing force applied by the hem roller and therefore imperfect hemming of the workpiece. Temperature variations in the environment (e.g., ambient plant temperatures) surrounding the roller hemming robot may also undesirably affect the accuracy of the hemming performed by the robot. Other factors that may also cause path variance of the robotic hemming roller include metal thickness tolerances, robot tolerances, and sealer dispense tolerances.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for monitoring pressure in a robotic roller hemming tool. For example, if the roller hemming tool includes a compressible fluid (e.g., gas) shock absorber, the present invention allows for the monitoring of the pressure in the shock absorber. The pressure in the shock absorber is related to the amount of force exerted by the roller hemming tool on a workpiece. Therefore, monitoring of the pressure in the roller hemming tool indirectly allows for the monitoring of the amount of force provided by the roller hemming tool. Based upon the monitored pressure in the roller hemming tool, the present invention allows for adjustment of the pressure in the roller hemming tool to maintain pressure within a prescribed, predetermined range, thereby assuring a constant hemming force.

More particularly, in one embodiment, a pressure monitoring robotic roller hemming apparatus includes a roller hemming tool including a compressible fluid shock absorber. A control panel is in fluid communication with the shock absorber. A pressure monitor is in fluid communication with the control panel and the shock absorber. The pressure monitor is operative to monitor pressure in the shock absorber.

The control panel may include a pressure relief valve in fluid communication with the shock absorber. The pressure relief valve is operative to adjust the pressure in the shock absorber. The control panel may also include a fluid input in fluid communication with the shock absorber. The fluid input allows for charging of the shock absorber. The fluid input may be a quick disconnect fitting. The pressure monitor may be electronically operated and may include a digital pressure display.

The roller hemming tool may include a support member. A guided slide member is received in the support and is slidable relative to the support. The shock absorber connects the slide member to the support member. A hem roller is rotatably mounted to the slide member. The control panel may be mounted on the support member. A robotic tool exchange head may be operatively connected to the support member, and the control panel may be mounted to the robotic tool exchange unit.

The pressure monitoring robotic roller hemming apparatus may also include a multi-axis controllable robot arm. The roller hemming tool may be operatively connected to the robot arm and the control panel may be mounted on the robot arm. The pressure monitor may be electrically connected to the robot arm. The pressure monitor may stops operation of the robot arm when pressure in the shock absorber is outside of a predetermined range of pressures.

A pressure monitoring method for robotic roller hemming includes providing a pressure monitor and a roller hemming tool including a compressible fluid shock absorber. The pressure monitor is connected in fluid communication with the shock absorber. Pressure is monitored in the shock absorber with the pressure monitor to obtain pressure measurements.

The pressure measurements may be displayed visually. The pressure may be adjusted in the shock absorber based upon the pressure measurements. The pressure in the shock absorber may be adjusted such that the pressure measurements are maintained within a predetermined range of pressures. Use of the roller hemming tool may be halted if the pressure in the shock absorber is outside a predetermined range of pressures.

A control panel may be provided, and the pressure monitor may be mounted on the control panel. The control panel may be mounted on the roller hemming tool. The control panel may include a fluid inlet for charging the shock absorber.

These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an environmental view of a robotic roller hemming apparatus including a multi-axis robotic arm and a roller hemming tool in connection with a pressure monitor in accordance with the invention; and

FIG. 2 is a perspective view of the roller hemming tool and pressure monitor.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings in detail, numeral 10 generally indicates a pressure monitoring robotic roller hemming apparatus. The hemming apparatus 10 includes a multi-axis controllable robot arm 12. A roller hemming tool 14 is operatively connected to an end of the robot arm 12. The robot arm 12 may include a tool exchange unit 16 at the end of the arm 12 for easy attachment of a tool such as the roller hemming tool 14 to the robot arm. The roller hemming tool 14 may also include a tool exchange head 18 that is cooperable with the tool exchange unit 16 for mounting the roller hemming tool 14 to the robot arm 12.

The roller hemming tool 14 may be of the type that includes a support member 20 having a slide bore 22. A compressible fluid shock absorber 24, such as a nitrogen gas shock absorber or similar, is disposed in the support member 20 and is extendable into the slide bore 22. A guided slide member 26 is received in the slide bore 22 and is slidable relative to the support 20. The slide member 26 is operatively connected to the shock absorber 24. A portion of the slide member 26 extends outside of the slide bore 22. A hem roller 28 is rotatably mounted to the slide member 26 near an end of the slide member outside of the slide bore 22. A retaining plate 30 is mounted to the support member 20 adjacent the slide bore 22 for retaining a portion of the slide member 26 in the slide bore and for limiting travel of the slide member out of the slide bore. The movement of the slide member 26 is tempered by the shock absorber 24 during the application of compressive forces against the hem roller 28.

By providing a reaction force, the compressible fluid shock absorber 24 helps to assure that a constant hemming force is applied by the hem roller 28 to nested panels that comprise a workpiece disposed on tooling despite variances in the path the hem roller follows along the workpiece. Further, in order to achieve satisfactory hemming together of the panels of a workpiece, the robot arm 12 must press the hem roller 28 of the roller hemming tool 14 against the workpiece with at least a certain minimum amount of force. Further, it is not desirable for the robot arm 12 to press the hem roller 28 against the workpiece above a certain maximum amount of force as this could lead to damage of the roller hemming tool 14 or the workpiece itself. The pressure exerted by the hem roller 28 against a workpiece is related to the fluid pressure within the shock absorber 24. For example, the fluid pressure within the shock absorber 24 may be initially set to a certain baseline pressure. When the hem roller 28 is properly engaged with a workpiece to perform hemming, the counterforce of the workpiece against the hem roller will cause the shock absorber 24 to partially compress, thereby increasing the pressure in the shock absorber. This pressure may be set as the baseline hemming pressure, and upper and lower pressure limits can be determined by adding and subtracting from the baseline pressure depending on hemming tolerances. If the pressure in the shock absorber 24 drops below the low pressure limit, this corresponds to a condition in which the hem roller 28 is not applying enough force against the workpiece. Similarly, if the pressure in the shock absorber 24 rises above the high (i.e., upper) pressure limits, this corresponds to a condition in which the hem roller 28 is applying too much force against the workpiece.

The robotic roller hemming apparatus 10 further includes a control panel 32 in fluid communication with the shock absorber 24, for example, via hose 33. The control panel 32 may be mounted on the support member 20 of the roller hemming tool 14. Alternatively, the control panel 32 may be mounted on a portion of the robot arm 12. A pressure monitor 34 is operatively connected to the control panel 32. The pressure monitor 34 is in fluid communication with the control panel 32 and the shock absorber 24 and is operative to monitor pressure in the shock absorber 24. The pressure monitor 34 may include a display for displaying the pressure measurements taken by the pressure monitor 34 so that a user may visually check the pressure level in the shock absorber 24. In one embodiment, the pressure monitor 34 is electronically operated and the pressure display is a digital display.

The pressure monitor 34 may be electrically connected to the robot arm 12. Alternatively, the pressure monitor 34 may be connected to programmable logic controllers which are in communication with the robot arm 12. In either case, if the pressure in the shock absorber 24 rises above a predetermined maximum pressure value or falls below a predetermined minimum pressure value, the pressure monitor 34 sends a shutoff signal to the robot arm 12, either directly or via the logic controllers. Hence, the hemming of a workpiece by the robot arm 12 is halted when the hemming pressure applied by the hem roller 28 is outside of a predetermined tolerance range.

The control panel 32 may also include a pressure relief valve 36 in fluid communication with the shock absorber 24. The pressure relief valve 36 is operative to adjust the pressure in the shock absorber 24, particularly to de-charge (i.e., bleed) fluid such as nitrogen gas from the shock absorber. The control panel 32 may further include a fluid input 38 in fluid communication with the shock absorber 24. The fluid input 38 allows for charging of the shock absorber 24 with fluid such as nitrogen gas. In one embodiment, the fluid input 38 may be a quick disconnect fitting that allows for easy connection and disconnection of a fluid supply hose to the control panel 32 for charging the shock absorber 24. This saves time in comparison to conventional charging methods in which the body of the roller hemming tool 14 would have to be disassembled to charge the shock absorber 24.

The fluid input 38 and pressure relief valve 36 may be used to adjust the pressure in the shock absorber 24 as follows. For initial startup of the roller hemming tool 14, a fluid supply hose may be connected to the fluid input 38. The shock absorber 24 may then be filled with fluid such as nitrogen gas to a pressure that is 100 psi above a target pressure. For example, if the target pressure in the shock absorber is 1900 psi, the shock absorber may be filled to a pressure of 2000 psi. The pressure in the shock absorber 24 can be monitored by the user by reading the display on the pressure monitor 34. After charging the shock absorber 24, the fluid supply hose may be disconnected from the fluid input 38. The shock absorber 24 may then be left at rest for approximately one hour to allow for stabilization of the pressure in the shock absorber due to changes in temperature and hence pressure expansion. After this resting period, nitrogen gas may be bled from the shock absorber 24 by opening the pressure relief valve 36 until the pressure in the shock absorber reaches a desired value, such as 1900 psi.

If the pressure in the shock absorber 24 later exceeds a predetermined maximum value during use of the roller hemming tool 14, such as due to an increase in ambient temperature in the work cell, the pressure in the shock absorber can be lowered via the pressure relief valve 36. Likewise, if the pressure in the shock absorber 24 later falls below a predetermined minimum value during use of the roller hemming tool 14, the pressure can be increased by connecting a fluid supply hose to the fluid input 38 and charging the shock absorber 24 until a desired pressure is reached. Alternatively, the shock absorber 24 can be overcharged and bled down to a desired pressure as described in the initial startup process above.

Although the invention has been described by reference to a specific embodiment, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiment, but that it have the full scope defined by the language of the following claims. 

1. A pressure monitoring robotic roller hemming apparatus comprising: a roller hemming tool including a compressible fluid shock absorber; a control panel in fluid communication with said shock absorber; and a pressure monitor in fluid communication with said control panel and said shock absorber, said pressure monitor being operative to monitor pressure in said shock absorber.
 2. The pressure monitoring robotic roller hemming apparatus of claim 1, wherein said control panel includes a pressure relief valve in fluid communication with said shock absorber, said pressure relief valve being operative to adjust the pressure in said shock absorber.
 3. The pressure monitoring robotic roller hemming apparatus of claim 1, wherein said control panel includes a fluid input in fluid communication with said shock absorber, said fluid input allowing for charging of said shock absorber.
 4. The pressure monitoring robotic roller hemming apparatus of claim 1, wherein said fluid input is a quick disconnect fitting.
 5. The pressure monitoring robotic roller hemming apparatus of claim 1, wherein said roller hemming tool includes: a support member; a guided slide member received in said support member and slidable relative to said support member, said shock absorber connecting said slide member to said support member; and a hem roller rotatably mounted to said slide member.
 6. The pressure monitoring robotic roller hemming apparatus of claim 5, wherein said control panel is mounted on said support member.
 7. The pressure monitoring robotic roller hemming apparatus of claim 5, including a robotic tool exchange head operatively connected to said support member, and said control panel being mounted to said robotic tool exchange unit.
 8. The pressure monitoring robotic roller hemming apparatus of claim 1, including a multi-axis controllable robot arm, wherein said roller hemming tool is operatively connected to said robot arm and said control panel is mounted on said robot arm.
 9. The pressure monitoring robotic roller hemming apparatus of claim 1, wherein said pressure monitor is electronically operated and includes a digital pressure display.
 10. The pressure monitoring robotic roller hemming apparatus of claim 1, including a multi-axis controllable robot arm, wherein said roller hemming tool is operatively connected to said robot arm, and wherein said pressure monitor is electrically connected to said robot arm; whereby said pressure monitor stops operation of said robot arm when pressure in said shock absorber is outside of a predetermined range of pressures.
 11. A pressure monitoring method for robotic roller hemming comprising the steps of: providing a pressure monitor; providing a roller hemming tool including a compressible fluid shock absorber; connecting said pressure monitor in fluid communication with said shock absorber; and monitoring pressure in said shock absorber with said pressure monitor to obtain pressure measurements.
 12. The pressure monitoring method of claim 11, including visually displaying said pressure measurements.
 13. The pressure monitoring method of claim 11, including adjusting the pressure in said shock absorber based upon said pressure measurements.
 14. The pressure monitoring method of claim 13, wherein the pressure in said shock absorber is adjusted such that said pressure measurements are maintained within a predetermined range of pressures.
 15. The pressure monitoring method of claim 11, including halting use of said roller hemming tool if the pressure in said shock absorber is outside a predetermined range of pressures.
 16. The pressure monitoring method of claim 11, including providing a control panel, wherein said pressure monitor is mounted on said control panel.
 17. The pressure monitoring method of claim 16, including mounting said control panel on said roller hemming tool.
 18. The pressure monitoring method of claim 16, wherein said control panel includes a fluid inlet for charging said shock absorber. 